A slug is a small decision you make once and live with for years, because the cost of changing it is paid in traffic.
The rules, in order of how much they matter
- Stable. Never change a published slug without a 301. This outweighs every other rule combined.
- Lowercase. URLs are case sensitive on most servers, so
/Aboutand/aboutare two pages with identical content — a duplicate you created by accident. - Hyphens, not underscores. Google treats a hyphen as a word separator and an underscore as a joiner, so
compress_pdfreads as one token. - Three to five meaningful words. Long enough to describe the page, short enough to read in a search result.
- No stop words unless removing them changes the meaning.
how-to-compress-a-pdfis fine;the-best-way-to-do-itis not. - ASCII only. Non-ASCII gets percent-encoded and becomes unreadable when pasted.
Everything below the first item is a preference. The first item is the one that costs money.
Why changing a slug is expensive
A URL accumulates value that does not transfer for free. Backlinks point at it, Search Console has history for it, it sits in bookmarks and in other people's documents, and Google has a record of its performance.
Change the slug and the old URL 404s. Every one of those links now points at nothing, and the new URL starts from zero.
A 301 redirect recovers most of it — the modern consensus is that a 301 passes essentially all ranking signal — but it adds a hop, and chained redirects compound. The bigger cost is operational: you now maintain a redirect forever, and forgetting one is how sites accumulate broken links nobody notices. Getting it right at publication is free.
Dates, numbers and categories
Three things people put in slugs that usually cost more than they give.
Dates. /2026/03/how-to-compress-a-pdf tells a reader the page is from March 2026, which makes it look stale by June. Worse, updating the article does not update the URL, so a current guide advertises an old date forever.
Numbers in a list post. /12-ways-to-compress-a-pdf locks you to twelve. Adding a thirteenth means either a false title or a slug change.
Deep category paths. /blog/pdf/compression/guides/how-to-compress-a-pdf adds no ranking value and guarantees a slug change whenever the taxonomy is reorganised, which it will be.
A flat structure — /blog/how-to-compress-a-pdf/ — survives reorganisation, which is exactly the event that otherwise forces a rename.
Transliteration is not the same as stripping
Handling non-ASCII characters has a right and a wrong answer, and most naive slug functions pick the wrong one.
Stripping produces nonsense: "Café Münchén" becomes caf-mnchn. Transliterating produces something readable: cafe-munchen.
It gets harder past Latin. German ß should become ss. Scandinavian ø is o and æ is ae. Cyrillic, Greek, Arabic and CJK need real transliteration tables, and for CJK there is often no good ASCII answer at all — a Chinese-language site is usually better served by percent-encoded native characters, which modern browsers display correctly.
The URL Slug Generator transliterates rather than strips, across Latin, Cyrillic, Greek and more, which is the difference between a readable slug and a row of consonants.
Trailing slashes and other duplicates
/about and /about/ are different URLs. So are http and https, www and apex, and /About and /about.
Serve one, redirect the rest, and make sure your canonical tag, your sitemap and your internal links all agree on which one. A site that links internally to one form while canonicalising another is sending a mixed signal for no benefit.
Pick a convention and enforce it at the server. Both trailing-slash styles are fine; being inconsistent is not.
Frequently asked questions
Should I use hyphens or underscores?
Hyphens. Google treats a hyphen as a word separator and an underscore as a joiner, so compress_pdf is read as a single token while compress-pdf is read as two words. This has been consistent guidance for many years.
How long should a slug be?
Three to five meaningful words. Long enough to describe the page, short enough to read in a search result without truncation. Drop stop words unless removing them changes the meaning.
Can I change a slug after publishing?
You can, but it costs. The old URL 404s, and every backlink, bookmark and citation points at nothing. A 301 recovers most of the ranking signal, but you maintain that redirect forever. Getting it right at publication is free.
Should I put the date in the URL?
No. It makes the page look stale within months, and updating the article does not update the URL — so a freshly revised guide advertises an old date permanently. Keep the date in the page metadata where it can change.
What about non-English characters?
Transliterate rather than strip. Stripping turns "Café Münchén" into caf-mnchn; transliteration gives cafe-munchen. For CJK there is often no good ASCII equivalent, and percent-encoded native characters are usually the better answer.
Does a trailing slash matter?
Only in that you must be consistent. /about and /about/ are different URLs and serving both is a duplicate. Pick one, redirect the other at the server, and make sure your canonical tags, sitemap and internal links all agree.